The research team led by Professor Herbert Herzog, head of the eating disorders laboratory at the Garvan Institute of Medical Research, looked at how stress or lack of it affected weight gain in mice on a high-calorie diet. They found that the mice in the stress environment gained more weight on the same diet than those in the non-stress group.

The team was left wondering what the root cause of the weight gain may be. After further investigation, they discovered a molecule called NPY was driving the stress eating, and when its production was turned off, weight gain decreased. While we cannot suppress the production of NPY, we may be able to limit its output by reducing stress and avoiding processed foods.

How? Well, it turns out that the production of NPY may be linked with our insulin levels as the stress-eating mice had higher insulin levels than those in the stress-free environment. These boosted insulin levels increased NPY levels, which triggered more stress eating and weight gain.

"Our findings revealed a vicious cycle, where chronic, high insulin levels driven by stress and a high-calorie diet promoted more and more eating," explains Professor Herzog. "This really reinforced the idea that while it's bad to eat junk food, eating high-calorie foods under stress is a double whammy that drives obesity," said Kenny Chi Kin Ip, Ph.D., the lead author of the study, in a statement.

You may be thinking, "From time to time I get stressed and eat unhealthy foods" and the truth is—most of us do. But this study isn't talking about a one-off treat but rather points out that chronic stress combined with eating processed foods is the big driver of unhealthy weight gain. So focusing on reducing your stress and decreasing your intake of processed foods (especially when stressed) may help mitigate this risk.